This invention relates to a high-density magnetic recording tape excellent in electromagnetic characteristics and running durability.
Magnetic recording media are widely used for recording all kinds of information including sound data, image data, and literal data. The recent innovation of technology has increased data storage capacity and data transfer rate and thus boosted the need for high-density recording. With this trend, magnetic recording media having high electromagnetic characteristics have been demanded. High reliability in repeated use of data and for data storage is also demanded. Accordingly, magnetic recording media are required to have satisfactory running durability as well as excellent electromagnetic characteristics. It is known that running durability of a magnetic tape media can be improved by properly designing a backcoating layer. Included among such attempts are roughening the surface of a backcoating layer by providing projections or adding coarse carbon particles of 0.1 xcexcm or greater. However, when a magnetic recording tape having a backcoating layer with such surface roughness is stored or handled for processing in form of a tape pack wound on a hub, the roughness can imprint itself in the magnetic layer under tape pack stresses, which can result in deteriorated electromagnetic characteristics. To overcome the roughness imprint problem, it has been attempted to smoothen the backcoating layer surface, but back side smoothening often causes poor tape pack wind quality. That is, entrapped air hardly escapes on tape winding, which can result in irregularities of a tape pack, such as popped strands of tape protruding from the edge of a pack.
The recent computer storage tape media are required to reduce in thickness for increasing recording capacity. Thickness reduction is achieved by, for example, reducing the thickness of a flexible support or the thickness of a non-magnetic layer provided in a particulate magnetic recording tape between a flexible support and a magnetic layer. When a pack of tape with an extremely thin flexible support has a poor wind quality with popped strands, the strands that stick out of the pack edge can be bent during storage, or the tape pack undergoes winding defects, such as cinching and spoking, which will lead to increased errors.
As an approach to improve electromagnetic characteristic by smoothening a backcoating layer to prevent roughness imprints, JP-A-11-259851 discloses a magnetic tape medium having a backcoating layer mainly comprising particulate titanium oxide and carbon black. Whereas the technique brings about improved back side smoothness and reduction of roughness imprints, the tape has a poor wind quality, and an increased error rate results after storage.
Hence, the related techniques have not provided a magnetic recording tape satisfactory in both electromagnetic characteristics and wind quality. Considering the increasing demand for further reduction in tape thickness, the state-of-the-art magnetic recording tapes are still unsatisfactory in electromagnetic characteristics and wind quality.
An object of the present invention is to provide a magnetic recording medium for high density recording which is substantially free from the roughness imprint problem and has excellent electromagnetic characteristics and a good wind quality.
As a result of extensive investigations, the inventors have found that a magnetic recording tape having a controlled surface roughness on its backcoating layer side and a moderate cupping satisfies both electromagnetic characteristics and tape wind quality.
The present invention provides a magnetic recording tape comprising a flexible support, a magnetic layer provided on one side of the support, and a backcoating layer on the other side of the support, wherein the backcoating layer has on its surface 10 to 200 projections having a height of 50 to 100 nm per 90 xcexcm side square as measured with an atomic force microscope (AFM) and 10 or fewer projections having a height greater than 100 nm and not greater than 500 nm per 90 xcexcm side square as measured with an AMF and the tape has a cupping of 3 to 20% of the tape width with convexity on the magnetic layer side. The cupping with convexity on the magnetic layer side will hereinafter be referred to as outward cupping.